add sidebar footer RSS readout (polls /memory every 30s)

Footer now shows "<bun-rss> · <tab-count>" sourced from the /memory
endpoint, polled every 30s. Color thresholds: orange warn at 2 GB Bun
RSS or 50 tabs; red bad at 8 GB or 200 tabs (matches the tab-guardrail
threshold landing in a later commit). The footer gives the user an
early signal that the cliff is forming, instead of only learning when
the OS OOM-kills the process.

Backoff per Codex's flag: if a poll takes > 2s response time the
sidebar drops to a 5-minute cadence until the next successful fast
poll. The diagnostic shouldn't add load to a browser that's already
unhealthy.

Start/stop is wired to the existing setServerInfo() hook so the timer
only runs while the sidebar is connected to a server.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

extension/sidepanel.css

@@ -1137,6 +1137,21 @@ footer {
   transition: color 150ms;
 }
 .footer-port:hover { color: var(--text-label); }
+.footer-mem {
+  color: var(--text-meta);
+  font-family: var(--font-mono);
+  font-size: 11px;
+  margin-right: 6px;
+  padding: 1px 6px;
+  border-radius: var(--radius-sm);
+  transition: color 150ms;
+}
+.footer-mem.warn {
+  color: #f59e0b;
+}
+.footer-mem.bad {
+  color: #ef4444;
+}
 .port-input {
   width: 56px;
   padding: 2px 6px;

extension/sidepanel.html

@@ -166,6 +166,7 @@
       <button class="footer-btn" id="reload-sidebar" title="Reload sidebar">reload</button>
     </div>
     <div class="footer-right">
+      <span class="footer-mem" id="footer-mem" title="Process memory + tab count from $B memory (polled every 30s, paused if slow)"></span>
       <span class="dot" id="footer-dot"></span>
       <span class="footer-port" id="footer-port" title="Click to change port"></span>
       <input type="text" class="port-input" id="port-input" placeholder="34567" autocomplete="off" style="display:none">

extension/sidepanel.js

@@ -292,6 +292,97 @@ async function connectSSE() {
   });
 }
 
+// ─── Memory Footer Readout ──────────────────────────────────────
+//
+// Polls /memory every 30s and renders "RSS: 1.4 GB · 12 tabs" in the
+// footer. Backs off to 5min if a poll takes > 2s (Codex flag — diagnostic
+// shouldn't add load when the browser is already unhealthy). Uses Bearer
+// auth like /refs above; /memory is a plain GET so EventSource semantics
+// don't apply.
+
+const MEM_POLL_FAST_MS = 30_000;
+const MEM_POLL_SLOW_MS = 5 * 60_000;
+const MEM_POLL_TIMEOUT_MS = 8_000;
+const MEM_POLL_SLOW_THRESHOLD_MS = 2_000;
+let memPollTimer = null;
+let memPollMode = 'fast'; // 'fast' | 'slow'
+
+function fmtBytesShort(n) {
+  if (typeof n !== 'number' || isNaN(n)) return '?';
+  if (n < 1024) return n + ' B';
+  if (n < 1024 * 1024) return (n / 1024).toFixed(0) + ' KB';
+  if (n < 1024 * 1024 * 1024) return (n / 1024 / 1024).toFixed(0) + ' MB';
+  return (n / 1024 / 1024 / 1024).toFixed(2) + ' GB';
+}
+
+function renderMemFooter(snapshot) {
+  const el = document.getElementById('footer-mem');
+  if (!el) return;
+  const bunRss = snapshot?.bunServer?.rss ?? 0;
+  const tabCount = Array.isArray(snapshot?.tabs) ? snapshot.tabs.length : 0;
+  el.textContent = `${fmtBytesShort(bunRss)} · ${tabCount} tabs`;
+  // Color thresholds: ~2 GB Bun RSS or 50 tabs is "watch this"; ~8 GB or
+  // 200 tabs is "this is the cliff" (matches the 200-tab guardrail).
+  el.classList.remove('warn', 'bad');
+  if (bunRss > 8 * 1024 * 1024 * 1024 || tabCount > 200) el.classList.add('bad');
+  else if (bunRss > 2 * 1024 * 1024 * 1024 || tabCount > 50) el.classList.add('warn');
+}
+
+async function pollMemoryOnce() {
+  if (!serverUrl || !serverToken) return { ok: false, slow: false };
+  const start = Date.now();
+  try {
+    const resp = await fetch(`${serverUrl}/memory`, {
+      headers: { 'Authorization': `Bearer ${serverToken}` },
+      signal: AbortSignal.timeout(MEM_POLL_TIMEOUT_MS),
+      credentials: 'include',
+    });
+    const elapsed = Date.now() - start;
+    if (!resp.ok) return { ok: false, slow: elapsed > MEM_POLL_SLOW_THRESHOLD_MS };
+    const snapshot = await resp.json();
+    renderMemFooter(snapshot);
+    return { ok: true, slow: elapsed > MEM_POLL_SLOW_THRESHOLD_MS };
+  } catch (err) {
+    const elapsed = Date.now() - start;
+    // Don't log every poll failure — common during browser restarts / restoring
+    // sessions. Only log on the slow path so the user sees something in the
+    // console if the diagnostic itself is misbehaving.
+    if (elapsed > MEM_POLL_SLOW_THRESHOLD_MS) {
+      console.debug('[gstack sidebar] /memory poll slow/failed:', elapsed, 'ms', err && err.message);
+    }
+    return { ok: false, slow: elapsed > MEM_POLL_SLOW_THRESHOLD_MS };
+  }
+}
+
+function scheduleNextMemPoll(delayMs) {
+  if (memPollTimer) clearTimeout(memPollTimer);
+  memPollTimer = setTimeout(async () => {
+    const { ok, slow } = await pollMemoryOnce();
+    if (!ok || slow) {
+      memPollMode = 'slow';
+      scheduleNextMemPoll(MEM_POLL_SLOW_MS);
+    } else {
+      // Successful + fast → back to fast cadence.
+      if (memPollMode === 'slow') memPollMode = 'fast';
+      scheduleNextMemPoll(MEM_POLL_FAST_MS);
+    }
+  }, delayMs);
+}
+
+function startMemPolling() {
+  if (memPollTimer) return; // already running
+  // Kick off an immediate poll so the footer populates within ~1s of sidebar
+  // open, instead of waiting 30s for the first cycle.
+  scheduleNextMemPoll(500);
+}
+
+function stopMemPolling() {
+  if (memPollTimer) {
+    clearTimeout(memPollTimer);
+    memPollTimer = null;
+  }
+}
+
 // ─── Refs Tab ───────────────────────────────────────────────────
 
 async function fetchRefs() {
@@ -893,9 +984,16 @@ function updateConnection(url, token) {
     chrome.runtime.sendMessage({ type: 'sidebarOpened' }).catch(() => {});
     connectSSE();
     connectInspectorSSE();
+    startMemPolling();
   } else {
     document.getElementById('footer-dot').className = 'dot';
     document.getElementById('footer-port').textContent = '';
+    const memEl = document.getElementById('footer-mem');
+    if (memEl) {
+      memEl.textContent = '';
+      memEl.classList.remove('warn', 'bad');
+    }
+    stopMemPolling();
     setActionButtonsEnabled(false);
     if (wasConnected) startReconnect();
   }